There are a number of presently available measuring devices for determining the distance between two points. Many of these devices include tape measures with digital readouts of the measurement obtained. These tape measures generally include a extendable tape or blade and some mechanism for determining the amount of the blade which has been extended. This mechanism in many instances includes an optical encoder which is comprised of encoding indicia and an optical reader for determining the positioning of the encoding indicia. A great many of these tape measures count a relative number of intervals and determine the measurement by the count. Some of these devices include code such as bar codes which have unique indica for every location on the tape. Thus, by reading the code, the exact location on the tape can be determined.
Each of these measuring devices have disadvantages. For example, with respect to the devices that simply count indica, the higher the resolution the more indica must be condensed into a given space. Further, the more indica which must be counted, the slower the operation becomes and the more chance that an error can be introduced into the count.
With respect to codes which identify absolute locations, again the more resolution required, the more code that must be condensed into a given area.
Many of the above devices require that the code be placed on the blade itself. Such arrangements have distinct disadvantages in that through use, the code can become worn or can be covered by foreign matter such as for example, dirt, paint and the like.
Certainly a number of other devices exist for making measurements. Just by way of example, for purposes of determining longer distances over open ground, measuring wheels positioned at the end of a long handle, are available. The operator walks along and holds the handle so that the measuring wheel is in contact with the ground. The device then records the number of revolutions of the wheel and provides a reading of the distance covered.